my periods started on 11 september.they lasted for 3 days.then in november ,there were no periods.On december 2 ,i had periods that lasted for 3-4 days ,but was normal bleeding.on december 27 i had periods only for 3-4 days.but i had periods again on jan 5 ,this time it lasted for 6 days with heavy bleeding .is it serious?wat should i do?